The present invention relates to a heatsink for a heat-producing device, such as an MOS-FET used in an AC adapter to effectively radiate heat.
In an AC adapter, an electronic device capable of resisting a large amount of current, such as a switching regulator, is used. Since electronic devices of such a type are also regarded as heat-producing devices which produce a large amount of heat, many of such electronic devices are configured to employ a so-called TO-220 package which can be attached to a heatsink and has an excellent heat radiation property.
An outer appearance of an example of an electronic device employing a TO-220 package (an electronic device 100) is shown in FIG. 8. As shown in FIG. 8, the electronic device of the TO-220 package type includes a plate part 112, three lead terminals 114 extending from the lower edge of the plate part, and a heat radiation plate 116 embedded in a first surface 112a of the plate part 112. The heat radiation plate 116 is made of metal having a high degree of heat radiation property.
An edge of the heat radiation plate 116 forms a projected part 116a projected upward from the upper edge of the plate part 112. In the projected part 116a, a through hole 116b which penetrates from a first surface 116c (i.e., a front-side on FIG. 8 identical with the first surface 112a of the plate part 112) to a second surface 116d (i.e., a back-side on FIG. 8) of the heat radiation plate 116 is formed. By inserting a screw through the through hole 116b, it is possible to fix the heat radiation plate 116 to a heatsink.
Since the electronic device 100 of the TO-220 package type has the above described shape, each of the plate part 112 and the heat radiation plate 116 is mounted to stand vertically with respect to a substrate when the electronic device 100 is mounted on the substrate via the lead terminals 114.
As disclosed in each of Japanese Utility Model Provisional Publications No. HEI 7-29894 (hereafter, frequently referred to as JP HEI 7-29894U) and No. SHO 60-167391 (hereafter, frequently referred to as JP SHO 60-167391U), a heatsink has a plate-like metal heastsink body provided along the first surface 116c (i.e., the first surface 112a of the plate part) of the heat radiation plate 116, and a clip configured to have a U-shaped cross section to closely contact the first surface 116c of the heat radiation plate 116 with the heatsink body. When the heat radiation plate 116 is fixed to the heatsink body 116 with a screw, the outer size of the AC adapter inevitably increases because in this case a top of the screw or a nut is situated on the outside. Therefore, for an AC adapter required to be compact in size, it is preferable that the electronic device is fixed to the heatsink body with a clip as disclosed in the above described publications.
As disclosed in JP SHO 60-167391U, it is desirable to provide an insulative plate between the heat radiation plate 116 and the heatsink body so as to prevent an unexpected current from flowing between the heat radiation plate 116 and the heatsink body. A heat-conductive and insulative silicon sheet may be provided in place of the insulative plate in such a manner that the silicon sheet covers the first surface 116c, the top of the projected part 116a and the second surface 116d of the heat radiation plate 116 in a shape of a letter U.
When each electronic device is fixed to the heatsink body with a clip, the clip is widened by attaching a jig to the clip, and the clip is fitted to each electronic device arranged on the heatsink such that the electronic device and the heastsink are inserted into arms of the clip. Then, by removing the jig from the clip, the clip is closed. Since the interval between the arms of the clip is smaller than the thickness of the plate part 112 in a normal state, when the jig is removed from the clip, the electronic device 100 is firmly fixed to the heatsink body by an elastic force of the clip. As shown in FIG. 8, since a step part 118 is formed in the upper part of the electronic device 100 by the second surface 116d of the heat radiation plate 116 and the top face 112b of the plate part 112, the arms of the clip need to be widened sufficiently so that the tips of the arms of the clip is not caught on the step part 118.